With the growth of print-on-demand market in the recent years, the demands for speeding up for electrophotographic techniques are ever more increasing. In view of the above, as a means for meeting the requirement of speeding up, a toner in which a polyester is used as a resin binder is used in order to fuse the toner on paper with less energy. However, if the toner as described above is used in printing for a long period of time in order to meet the requirement of speeding up, there are some disadvantages, such as the triboelectric charges gradually increase and the image density is lowered.
In view of the above, in order to overcome these disadvantages, a method of stabilizing triboelectric charges by using a combination of a negatively chargeable charge control agent and a positively chargeable charge control agent is proposed (see JP-A-Sho-63-68853 and JP-A-Hei-10-221879). In addition, a method of stabilizing triboelectric charges by using a combination of a polyester obtained from fumaric acid having a smaller content of a low-molecular weight component, and positively and negatively chargeable charge control agents (see JP-A-2005-37926).